This invention pertains to pressure transducers and methods of assembly and calibration of pressure transducers.
Pressure transducers are used in various types of applications. One application in the automotive field where a pressure transducer is used is in an engine fuel control system where the transducer senses barometric pressure and provides a corresponding electrical signal for use by the engine control system in correcting volumetric fuel delivery for variations in atmospheric presure. A specific example of such an application is an electronic fuel metering system of the type disclosed in U.S. Pat. No. 3,935,851, assigned to the same assignee as the present application. Another example of usage for a pressure transducer in the automotive field is sensing engine intake manifold vacuum and providing a corresponding signal for use by an electronic control, such as an electronic spark timing control.
An undesirable feature of prior pressure transducers which have been produced for the automotive industry is that such transducers are relatively high cost devices. Typical prior devices incorporate such structure as linear variable differential transformers, silicon strain gages and capacitancetype sensors. There are a number of reasons for such inherent high manufacturing costs. For one, temperature compensation is difficult to obtain without going to fairly sophisticated electronic control. For another, the motion produced by transducers which use a diaphragm-type aneroid is relatively small, and this makes dimensional tolerances very critical. Further, control of the rate and offset calibrations of these devices has typically been done by very careful control of the aneroid assembly which is a relatively expensive manufacturing process.
In contrast, the present invention is directed to a new and unique pressure transducer which overcomes the foregoing disadvantages of prior devices. As a result, a pressure transducer embodying principles of the present invention affords the opportunity for reduced manufacturing cost while retaining the required degree of accuracy. The transducer has a sensing element which exhibits a comparatively large amount of motion over its operating range, a feature which is beneficial in minimizing the adverse effects of dimensional tolerance variations in the structure of the transducer. The invention also employs a new and unique means for adjusting and calibrating a pressure transducer with expediency and accuracy. An advantage of the invention is that it can reduce inaccuracies caused by temperature changes. An additional advantage is that the transducer has no levers or pivots which tend to introduce hysteresis.
The foregoing features and advantages and benefits of the present invention, along with additional ones, will be seen in the ensuing description and claims which are to be considered in conjunction with the accompanying drawings which disclose an exemplary but presently preferred embodiment of pressure transducer embodying principles of the present invention according to the best mode presently contemplated in carrying out the invention.